1. Field of the Invention
The present invention relates to a servo press moving up and down a slide by a toggle mechanism and an operating method thereof.
2. Description of the Related Art
Conventionally, there has been known a servo press having a toggle mechanism (also called as a knuckle mechanism). The toggle mechanism converts a linear motion taken out by converting a rotation of a servo motor, into an upward and downward motion of a slide.
Generally, the toggle mechanism is provided with a first link and a second link in which one ends thereof are rotatably connected to each other in a connecting point, the other end of the first link is rotatably connected to a part of a crown, the other end of the second link is rotatably connected to the slide, and a driving link is rotatably connected to the connecting point between the first link and the second link.
In the toggle mechanism having the structure mentioned above, since a toggle shape constructed by the first link and the second link is deformed so as to open and close by moving forward and backward the driving link with respect to the first and second links by a direct acting actuator, the slide is moved up and down. Since it is possible to make a sliding speed near a bottom dead point slower in comparison with a crank mechanism by having the toggle mechanism mentioned above, it is possible to satisfy a demand in each of a moving section (high speed and low pressure) and a pressurizing section (low speed and high pressure).
Above described servo presses having the toggle mechanism are disclosed in Japanese Unexamined Patent Publication No. 2002-103089 and Japanese Unexamined Patent Publication No. 2001-300778.
A servo press in Japanese Unexamined Patent Publication No. 2002-103089 is structured such as to drive a toggle driving means having a ball screw by a servo motor, and drive a toggle mechanism (called as a knuckle mechanism in Japanese Unexamined Patent Publication No. 2002-103089) constituted by two links connected by a connecting pin by the toggle driving means, thereby moving up and down a slide via a plunger by bending and stretching motion of the toggle mechanism. The toggle mechanism of the servo press is constituted by a so-called one-stage toggle in which one toggle effect (a force amplification effect) can be obtained.
A servo press in Japanese Unexamined Patent Publication No. 2001-300778 is provided with a square multi-thread rotationally driven around an axis in a vertical direction, an elevating body engaging with the square multi-thread and being movable up and down together with a rotation of the thread, and a multi-link mechanism connecting between the elevating body and a slide. The multi-link mechanism has a pair of first links in which respective one ends are rotatably connected to right and left sides of the square multi-thread, a pair of right and left second links in which respective one ends are rotatably connected to a press frame, and a pair of right and left third links in which respective one ends are rotatably connected to a slide, and the other ends of the right and left first to third links are rotatably connected to each other. The slide is moved up and down via the elevating body and the multi-link mechanism by rotating the square multi-thread. The toggle mechanism of the servo press is constituted by a so-called two-stage toggle in which two toggle effects can be obtained.
The servo press of Japanese Unexamined Patent Publication No. 2002-103089 mentioned above employs the one-stage toggle, and the servo press of Japanese Unexamined Patent Publication No. 2001-300778 employs the two-stage toggle. Accordingly, it is possible to obtain a high speed in the moving section of the slide, and obtain a low speed and a high pressure in the pressurizing section.
However, in these servo presses, in order to obtain the higher speed in the moving section of the slide, and obtain the higher pressure in the pressurizing section near the bottom dead point, it is necessary to enlarge a capacity of the motor. Accordingly, there is a problem that the motor is enlarged in size and a cost is increased.
Further, in the servo press of Japanese Unexamined Patent Publication No. 2002-103089, the direct acting portion (the toggle mechanism) is arranged at a height corresponding to an intermediate position of the toggle mechanism. Accordingly, it is necessary to interpose a plunger (an extension link) between the slide and the direct acting portion so as to prevent the direct acting portion and the slide from being interfered with each other at a time when the slide is moved up, that is, so as to secure a stroke. The plunger mentioned above is essentially an unnecessary element in a mechanism for driving the slide. In other words, there is a problem that the essentially unnecessary element is included.
Further, in the servo press of Japanese Unexamined Patent Publication No. 2001-300778, since the square multi-thread is vertically arranged, a total height of the apparatus becomes high. In the press machine, it is required to secure a fixed stroke or more while suppressing the total height of the apparatus, however, in the servo press of Japanese Unexamined Patent Publication No. 2001-300778, there is a problem that it is hard to satisfy such a request.